With high Federal CAFE requirements and a desire to reduce pollution, fuel economy in a vehicle becomes ever more important. A known technique of improving fuel economy and reducing emission output is to deactivate half of the engine cylinders by deactivating the corresponding valves during part load engine operation when the output requirement is low. V6, V10 and some other overhead valve engine configurations have dual banks of cylinders, each with their own camshafts, and a firing order such that the firing alternates from bank to bank.
The invention provides on these types of OHC engines an alternative method of valve train deactivation by the selective uncoupling of one of the camshafts of one of the banks from the engine driven crankshaft sprocket during part load engine operation. The operating strategy includes startup on half the cylinders down to ambient temperature levels where half the cylinders can still sustain engine operation.